1. Technical Field
This invention relates generally to methods, devices, and systems used in the field of cardiovascular medicine for clinically assessing of a patient's health condition. More particularly, it relates to a new and improved system and method for monitoring cardiac blood flow balance between the right and left heart chambers based on arterial pulse waveforms representing blood pressure or flow or constituent concentration per cardiac cycle.
The description below is merely provided for general background information and for assisting in understanding the technical field to which the present invention is related. As is generally known in the art, the circulatory system in human beings is responsible for transporting oxygen and other nutrients to the cells of the human body. The circulatory system includes a heart, arteries, capillaries, and veins. In a healthy patient, the heart pumps blood with a certain pressure and volume so as to ensure that proper blood circulation is realized within the human body. Therefore, a discussion of the blood flow in the heart and congestive heart failure (CHF) will now be provided initially.
With attention directed to FIG. 1 of the drawings which is labeled “Prior Art”, there is illustrated a diagram of the cardio-vascular system and its cycle. The heart 2 consists of four chambers; namely, the right atria 4, the right ventricle 6, the left atria 8 and the left ventricle 10. The right atria 4 receives carbon dioxide-filled blood which is returning from the body through the superior vena cava 12 and the inferior vena cava 14 where they join in the central venous. The right ventricle 6 receives the blood from the right atria 4 via a tricuspid valve 16 located between the two chambers. The right ventricle 6 pumps the blood via a pulmonary valve 22 into the pulmonary artery 18 which branches into the right pulmonary artery 18(a) for carrying the blood to the right lung 20(a), and the left pulmonary artery 18(b) for carrying the blood to the left lung 20(b). After receiving oxygen in the lungs 20(a) and 20(b), the oxygen-filled blood is returned to the left atria 8 of the heart 2 via the right pulmonary vein 24(a) and the left pulmonary vein 24(b). The blood is then passed into the left ventricle 10 via mitral valve 26. Next, the left ventricle 10 pumps the blood via the aortic valve 30 into the aorta 28 which branches into the ascending aorta for delivery throughout the upper body 31(a) heads and arms, and the descending aorta 31(b) for delivery throughout the lower body including the trunk and legs via the network of arteries, capillaries, and finally returned to the heart 2 via the superior vena cava 12 and the inferior vena cava 14, which both merge into the center venous 32. Both the right atria 4 and the left atria 8 pump simultaneously, and both the right ventricle 6 and the left ventricle 10 pump simultaneously. In every pumping cycle, each chamber undergoes an expansion cycle called diastole followed by a contraction cycle called systole. On the ECG waveform, the Atrial diastolic phase extends between the S in the QRS complex until the start of the following P wave, while atrial systole is between the start of the P wave and extends through the following S in the QRS complex. Similarly, the Ventricular systolic phase is between the R in QRS-complex and the following end of the T-wave, while ventricular diastolic phase is between end of the T-wave and the following R in the QRS-complex. The atrial systolic phase occurs mostly during ventricular diastolic phase with a small fractional overlap to ventricular systole, while the atrial diastolic phase starts with the ventricular systolic phase but also extends and overlaps a substantial portion of the ventricular diastolic phase. Atrial diastolic phase has a longer duty cycle as compared to Atrial systolic phase.
The left ventricle (LV) and the right atrium (RA) are connected in a supply and demand relationship. Also the right ventricle (RV) and the left atrium (LA) are connected in a supply and demand relationship. A balance therefore must be achieved for each supply and demand relationship between the LV and RA (termed Left Right Balance (LRB)), and between the RV and LA (termed Right Left Balance (RLB)). Similarly a balance must be achieved across the two pairs of supply and demand relationships (LV,RA) and (RV,LA). Such a balance of the LRB and RLB balance parameters is termed the Systemic-Pulmonary circulation balance parameter (SPB) indicating a shift of the blood supply towards the systemic portion of the circulatory cycle or the pulmonary portion of the circulatory cycle. When the SPB is normal, this can be used to validate assumptions of the Fick equation that the left and right ventricular cardiac output on average are equivalent, as presumed in healthy individuals.
In healthy human beings, the right heart's cardiac output (RCO) blood flow is presumed equivalent to the left heart's cardiac output (LCO), on average, since the cycle must maintain steady blood flow through out the circulatory system. However, this is not true in patients with certain types of heart disease. For example, an infarction or arrhythmia on one side of the heart may lead to insufficiency in balance between the RCO and LCO. Thus, cardiac output (CO) is an important indicator not only for the diagnosis of the certain types of heart disease, but also for the continuous monitoring of a patient's health condition.
One basis for most common cardiac output-measurement systems is given by the well-known equation CO=HR×SV, wherein CO is the cardiac output defined as blood flow in liters/min and is equal to the heart rate (HR) times the stroke volume (SV). The stroke volume is usually measured in liters, and the heart rate is usually measured in beats per minute. This equation explains that the amount of blood the heart pumps out over a unit of time (e.g., a minute) is simply equal to the amount it pumps out on every beat (stroke) times the number of beats per time unit.
If the right heart's cardiac output RCO (blood flow out of the right ventricle into the pulmonary artery) mostly exceeds the left heart's cardiac output LCO (blood flow out of the left ventricle into the aorta) then blood accumulation in the pulmonary system (lungs) is evident, and which may lead to congestive heart failure (CHF). Similarly, if the left heart's cardiac output LCO mostly exceeds the right heart's cardiac output RCO then blood accumulation is evident in the body's vascular system and tissue fluids will accumulate leading to inflation in tissue or vascular diseases such as high blood pressure, and potentially may play a factor in the development of varicose veins. Therefore, a measure of the balance between the right heart's and left heart's cardiac outputs is necessary for monitoring the overall health of the cardiovascular and pulmonary systems.
In the inventor's view, the cardiac system is basically a control system with two primary objectives. The first primary objective is to maintain oxygen delivery to the tissue via adequate perfusion (blood flow and blood pressure), which is accomplished by varying the cardiac parameters such as heart rate, stroke volume, and contractility, and blood pressure. The heart's second primary objective is to maintain a target blood flow balance between the right and left heart chambers.
While the cardiac output balance between the right heart and the left heart chambers is an important clinical parameter for the purposes of diagnosing, treating, and monitoring cardiovascular disease, the conventional prior art techniques, such as thermodilution or dye dilution, for measuring this balance however requires intravascular or intramyocardial instrumentation which carries significant risks to the patient that includes increased perioperative morbidity and mortality, and increased long-term risks, such as stroke and pulmonary embolism. Additionally, intravascular instrumentation can only be performed by highly trained specialist which severely limits the availability of qualified physicians capable of implanting the device, thereby increasing the cost of the procedure.
Also, the estimation of the balance between right heart's and left heart's cardiac outputs by these conventional methods would necessitate measurement of both left and right cardiac outputs independently and then comparing (for example by subtraction or ratio or so any other means of comparison) both to obtain the measure of the balance. In addition, less invasive methods are also known in the prior art, but they have proved to be less accurate in their measurements. Further, the traditionally non-invasive methods are not able to distinguish between the left cardiac output and the right cardiac output.
2. Prior Art
In U.S. Pat. No. 5,211,177 to Chesney et al., there is disclosed a vascular impedance instrument which includes a transducer to obtain a digitized arterial blood pressure waveform. The digitized data is used to determine cardiac output and to subsequently obtain measurements of impedance parameters using the modified Windkessel model of the arterial system. The instrument is used as an aid in diagnosing, treating and monitoring patients with cardiovascular disease.
In U.S. Pat. No. 7,651,466 to Hatib, Feras et al., examines the pulse contour of arterial pressure pulses to map using an linear model (Windkessel method) into a flow pulse for purposes of estimating cardiac output. This does not take into account the relationships between the ventricular arterial supply and atrial venous demand on the shape of the pressure waveform, but it analyzes the segment component of waveform prior to the onset of the interaction of the atrial venous demand on the ventricular arterial supply. Calibration of the model compliance parameters are required for estimating the dynamic relationship between blood pressure and flow rate.
In U.S. Pat. No. 8,282,564 to Parlikar, et. al., Similarly uses a lumped compliance model to model (Windkessel method) the relationship between arterial pressure and flow rate to estimate cardiac output, again the interaction effects between the ventricular arterial supply and atrial venous demand are not considered on the shape or morphology of the arterial pressure waveform.
In EU Patent No. EP1,848,330 B1 to Bennett, Tommy, et. al. Uses right ventricular pressure (RVP) pulse contour to estimate the stroke volume using a Windkessel pulse contour method. This method uses the full dynamic waveform information in the RVP to relate to the stroke volume information. It does not selectively choose specific landmarks on the pressure waveform to relate to volume information in a static method as in this invention.
In U.S. Pat. No. 5,368,040 to James Carney, describes analysis of ventricular pressure waveform and derives landmarks identified from first and second derivative inflection points or zero-crossing points or as related to features on an ECG waveform. It does not attempt to map these pressure values to volumetric information for purposes of estimating cardiac volumes or flow rates given pressure information.
The determination of the oxygen content of the blood based on the spectral characteristics of hemoglobin and oxyhemoglobin. Wood (U.S. Pat. No. 2,706,927) described a method using two wavelengths of light. Shaw (U.S. Pat. No. 3,638,640) improved this procedure by using more wavelengths of light. This technique was made significantly more practical by use of the modulation caused by the pulse as invented in 1972 by Aoyagi (Japanese Application 947714, April 1979). Improvements were described by Nielsen (U.S. Pat. No. 4,167,331) and Flower (U.S. Pat. No. 4,863,265). These methods rely on the ratio (R) of normalized variable component of the red light to its infrared light counterpart to determine a ratio of absorbance due to hemoglobin color which is dependent on oxygen binding or saturation. The method suffers from sensitivity to motion artifacts, and inherent variability across subject's response curves. Calibration to empirically derived lookup table is necessary to map the R ratio to validated oxygen saturation values. This approach suffers from insufficiently describing the relationship between the red and infrared plethysmography waveforms and underestimates the model order and model structure that describe the dynamic relationship between the red and infrared signals, as it presumes the relationship as a simple linear scalar ratio factor R. It also only uses the measured arterial pulse waveform and does not apply the ratio R method to the arterial pulse primary components of arterial supply (represented by full arterial pulse) and venous demand (represented by arterio-venous pulse) waveforms as described herein.
The inventor of the instant invention, however, is not aware of system for measuring of a cardiac blood flow parameter between the left chamber of the heart and the right chamber of the heart that uses a sensor device to measure one of blood pressure and blood flow and blood constituent concentration of a patient so to generate an arterial pulse signal, a process unit for generating a full arterial pulse signal from the arterial pulse signal, the processor unit generating an arterio-venous pulse signal by subtracting the arterial pulse signal from the full arterial pulse signal, and the processor unit generating the balance parameter by calculating the ratio of the area under the curve of the arterio-venous pulse signal, measured by integration over the cardiac cycle, to the area under the curve of the full arterial pulse signal, measured by integration over the same cardiac cycle. The area under the curve can be calculated by the integration of the pulse waveform using any integration method, preferably trapezoidal approximation method. Whereas the DC offset can be either included in the integration, or normalized, or removed by subtraction. The use of the word pulse throughout herein is used to more generally indicate the measured signal of type such as a blood pressure or blood flow rate or blood constituent concentration waveform.
Therefore, it would be desirable to provide a system and method for measuring of a cardiac blood flow parameter between the left chamber of the heart and the right chamber of the heart useful in creating a clinical assessment of a patient's health condition. Further, it would be expedient that the system of the present invention be capable of performing as a clinically useful tool for the purpose of diagnosing, treating and monitoring the performance and function of a patient's liver, heart, lungs, brain, kidneys and other organs of the body. The present invention represents a significant improvement over the aforementioned prior art which is hereby incorporated by reference in their entirety.